This invention relates to microwave transistor packages having very low parasitic inductance and capacitance associated with the leads thereof.
High frequency semiconductor packages are used for holding high frequency semiconductor components, such as microwave transistors and the like, and providing readily available terminals for connection to other components. For such packages it is important to reduce parasitic coupling between terminals, which parasitic coupling degrades the performance of the transistor. At microwave frequencies, the parasitic inductances and capacitances associated with the leads of the semiconductor packages limit the gain and bandwidth of the transistors housed therein. The critical inductive parasitic components in a microwave transistor package are the inductance of the input terminal and the inductance of the terminal connected to the ground. The inductance of the terminal connected to the ground may be particularly critical, because it is inaccessible, and can not be turned out with additional external components.
A variety of high frequency semiconductor packages utilized in the past have suffered from a variety of shortcomings usually in bonding to lead terminals at different heights, and involving a plurality of electrically conducting members and electrically insulative members bonded together, requiring expensive precision components in construction of the package.
A couple of high frequency semiconductor packages having a structure which provides excellent high frequency performance and yet require a small number of parts in the construction thereof are described in U.S. Pat. No. 3,784,884 and pending U.S. patent application, Ser. No 383,872, both assigned to the assignee of the present invention. The structure described in the above patent requires coined bonding rails extending from the header in one embodiment thereof which requires an expensive coining apparatus and also requires the use of expensive material such as silver for the header. Furthermore, design modifications for this prior art high frequency semiconductor package to accommodate larger semiconductor chips usually require extensive redesign of most of the package parts and fabrication apparatus, thereby making design modifications extensive. The pending disclosure is an improvement over the former in that the two bonding rails used for the low inductance, low reactance bonding are made of cylindrical wires.
However, both of the aforementioned prior art disclosures describing semiconductor packages use a square or rectangular format of construction. Structurally, both of these designs exhibit several deficiencies. The rectangular format induces mechanical stress concentrations at the interior corners of the ceramic member. This may result in fracturing the corners during package assembly. To overcome this, it is necessary to include a molybdenum window frame member in the construction to serve as an expansion buffer between the ceramic and copper base. Furthermore, because of the delicate nature of the wire rails and the difficulty of retaining them in position along with a metallized die bond insulator during brazing of the components together, there has been a higher yield loss due to poor positioning of these components than is desirable.
Thus, a need exists to solve many of the aforementioned shortcomings of the prior art by providing a less complex and lower cost semiconductor package.